1. Field of the Invention
The present invention relates to a highly conductive carbon nanotube having bundle moieties with ultra low apparent density less than 0.01 g/cc. More specifically, this invention relates to a highly conductive carbon nanotube prepared by following preparation steps of i) preparing the sphere shape of metal catalyst by spray pyrolysis of catalytic metal precursor solution including low molecular weight polymer, ii) synthesizing carbon nanotube using carbon source and obtained metal catalyst according to thermal chemical vapor deposition method; and iii) obtaining a highly conductive carbon nanotube having bundle moieties with ultra-low bulk apparent density.
Further, a carbon nanotube having bundle moieties prepared by thermal chemical vapor deposition method using specific metal catalyst composition by spray pyrolysis of catalytic metal precursor solution shows 0.003˜0.010 g/cc of bulk apparent density, 3˜15 nm of diameter of carbon nanotube, 5˜100 μm of vertically aligned bundle diameter, and 10˜500 μm of bundle length. Further, a carbon nanotube having bundle moieties prepared by present method can be used for manufacturing highly conductive carbon nanotube-polymer complex when carbon nanotube of present application is mixed with polymer.
2. Description of Prior Art
Carbon nanotube was firstly disclosed by Dr. Iijima in Nippon Electric Company (NEC) by arc discharging the carbon rod containing metal catalyst (S. Iijima, Nature, 354, 56 (1991)). The further studies of carbon nanotube disclosed that carbon nanotube shows diverse and advantageous physical and chemical properties. The technical developments in controlling the structure of carbon nanotube let it be applied to various fields of industries, such as, reinforcing agent of polymer, pharmaceuticals, storage of energy, catalyst support for polymer synthesis.
A research group of Baker and N. M. Rodriguez in the United States has specifically developed the crystalline structure of carbon nano materials (J. Mater. Res., Vol 8: 3233˜3250, 1993). As preparation methods of carbon nanotube, an arc discharge method, a laser ablation method, a catalytic growing method and a plasma method have been described in following documents: that are, R. E. Smalley et al., J. Phs. Chem., 243, 49(1995); M. Endo et al., Carbon, 33, 873(1995); U.S. Pat. No. 5,424,054; Chem. Phys. Lett., 243, 1-12(1995); Science, 273: 483-487(1996); and U.S. Pat. No. 6,210,800.
For a commercial use of carbon nanotube, it is very important to produce high quality of carbon nanotube in a low cost. It has been known that structural control of diameter or length of carbon nano material can be accomplished by understanding of transition metal, catalyst support materials and interaction between transition metal and catalyst support materials.
In PCT International publication No. WO 2006/50903 ‘Catalyst for producing carbon nanotubes by means of the decomposition of gaseous carbon compounds on a heterogeneous catalyst’, it has been disclosed that the transition metal catalyst composition comprising Mn, Co, optionally Mo and a support material enables to produce carbon nanotube having 3˜150 nm of diameter in a high catalytic yield. However, there is no specific description about the role of catalyst particle shape for enhancing the electro conductivity of carbon nanotube in the dispersed carbon nanotube solution.
In Korean Early Patent Publication No. 10-2006-18472 ‘Process for preparing carbon nanotube using the mechano-chemical treated catalyst’, carbon nano fiber prepared by a chemical vapor deposition method using acetylene as a carbon source in the presence of mechano-chemical treated support catalyst comprising Ni and Mg support has been disclosed.
In Korean Early Patent Publication No. 10-2005-78596 ‘Purification method of carbon nanotube and preparation method of carbon nanotube’, carbon nanotube prepared by a plasma chemical vapor deposition method has been disclosed. Further, in this preparation method, the plasma chemical vapor deposition method comprises i) substrate preparation step for growing carbon nanotube; ii) growing step for carbon nanotube on the said substrate; and iii) purification step of carbon nanotube using plasma of inert gas has been disclosed. However, carbon nanotube obtained using this method cannot afford high electro conductivity in the dispersed carbon nanotube solution or polymer matrix.
The preparation method for the synthesis of carbon nanotube disclosed in various technical documents or patents can be specified by the kind and ratio of transition metals and the shape and size of support materials included in catalyst composition. Regarding the preparation of catalyst composition, it has been described in following documents. P. E. Anderson et al., J. Mater. Res., 14(7), 2912(1999); and R. J. Best, W. W. Russell, J. Am. Chem. Soc., 76, 838(1974). Nonetheless, it is still required to develop a catalyst composition to enhance the catalytic productivity as well as to realize structural characteristics of carbon nanotube by controlling the numerous variables regarding catalyst synthesis.
However, the shape of carbon nanotube for effective dispersion in the solution has never been developed or disclosed in the prior art. Further, the characteristics of suitable catalyst for highly conductive carbon nanotube have not been disclosed regardless of batch or continuous synthesis process.
Most of catalyst for the synthesis of carbon nanotube has a shape of sphere or fine particle. In the field of nano technology, sol-gel, co-precipitation, hydrous pyrolysis, and/or flame metal combustion method has been adopted for preparing catalyst precursor, followed by drying the obtained catalyst precursor using freeze drying or spray drying for minimizing the aggregation of catalyst particles. On the other hand, the vertically aligned growth of carbon nanotube applied from semiconductor manufacturing process has been tried. However, this synthetic method cannot be regarded as suitable method for coating solution or polymer compound of carbon nanotube.
Entangled type of carbon nanotube aggregate has been required to be changed into fibrous type of carbon nanotube for being dispersed in solution or polymer matrix. For this purpose, chemical treatment of surface for enhancing dispersibility or mechanical treatment of carbon nanotube with high energy has been required. However, it is not easy to maintain the native characteristics of carbon nanotube during such chemical or mechanical treatment or carbon nanotube.
Vertically aligning technology has been suggested by Hata Research Group in Japan on the basis of super-growth of carbon nanotube in the limited bundle surface. Such vertically aligned bundle type of carbon nanotube may be advantageous in the dispersion of carbon nanotube rather than entangled type of carbon nanotube particles. Further, if such aligned bundle type of carbon nanotube can be manufactured according to thermal chemical deposition method, this aligned bundle type of carbon nanotube can be much advantageous in solution dispersion or polymer compounding of carbon nanotube, because less energy may be required for dispersion.
Such high dispersion mechanism may proceed step by step from macro size level to micro size level, eventually to accomplish nano size level dispersion as shown in FIG. 5.
However, carbon nanotube prepared according to conventional method may cause the structural decomposition of carbon nanotube in the course of cutting-off or crushing the carbon nanotube to be dispersed in the solution or polymer matrix as well as loss of conductivity of carbon nanotube.
Therefore, the inventors of present invention have developed a highly conductive carbon nanotube having bundle moieties with ultra-low bulk density by controlling the metal catalyst composition and synthetic steps of preparation process for carbon nanotube. Eventually, the obtained carbon nanotube having bundle moieties of present invention has following properties; i) apparent density of carbon nanotube is 0.003˜0.010 g/cc, ii) fibrous diameter is 3˜15 nm; iii) diameter of vertically aligned bundle is 5˜100 μm; and iv) the length of bundle is 10˜500 μm.
Further, the inventors of present invention have also developed a mass production method for carbon nanotube having bundle moieties, using specifically prepared metal catalyst composition. The metal catalyst composition comprises Al and Mn as well as main catalyst metal, wherein the amount of Mn as to the amount of Al is in the range of 0.1˜20 wt %. Further, the metal catalyst composition contains a small portion of low molecular weight polymer to avoid the aggregation of metal catalyst composition powder during the spray pyrolysis process. On the other hand, the carbon nanotube having bundle moieties of present invention can be obtained by controlling the synthetic steps of preparation process for carbon nanotube with following physical properties; i) apparent density of carbon nanotube is 0.003˜0.010 g/cc, ii) fibrous diameter is 3˜15 nm; iii) diameter of vertically aligned bundle is 5˜100 μm; and iv) the length of bundle is 10˜500 μm.